The present invention relates to electromechanical programmer/timers utilized for sequentially activating at least one and usually a plurality of electrical switches for a selective program interval. Programmer/timers of this sort are commonly employed for appliances such as clothes washing machines, dishwashers, microwave ovens and other appliances wherein it is desired for the machine user to select a desired program interval for the appliance operation; and, upon such selection a timing motor provides advancement of a cam track for sequentially actuating the machine control function switches during time-out of the selected interval.
Typically, electromechanical appliance programmer/timers utilize a subfractional horsepower synchronous timer motor driving either a continuous drive to the cam through a speed reducer, or employ an indexing mechanism such as a ratchet wheel engaged by a periodically advanced and retracted pawl.
Heretofore, differing rates of advance in appliance programmer/timers have been provided by utilizing ratchet teeth of varying depth disposed about the advance ratchet with blocking means, usually comprising a masking ratchet wheel, to permit the pawl to engage the notches of greatest depth only upon selected multiples of the advanced pawl stroke, thus providing alternate rates of intermittent advancement of the cam ratchet. However, the fastest rate of advancement in such arrangements is determined by the number of teeth having the greatest minor diameter on the ratchet wheel with the teeth of lesser major diameter providing a substantially slower rate of advancement. Where continuous drive for the cam is employed via means of a motor speed reducer, it has heretofore been the practice to shift or change gearing in order to provide alternate rate of advance.
However, in certain appliance applications, it is desired to provide a relatively slow rate of advancement utilizing the well known ratchet and pawl cam indexing technique; however, it is also desired to provide a substantially more rapid rate of advancement of the cam for certain selected portions of the program time out interval. Therefor, utilizing only a ratchet and pawl advance technique for the cam track limits the resolution of the cam track by virtue of the pitch of the teeth required to provide the desired maximum rate of advance. If the pitch of the teeth for the ratchet is chosen for the desired maximum rate of advance, within the allowable diameter for the ratchet, problems have been encountered in providing the desired resolution of the cam functions within a single revolution of the rotary cam track.
Therefore, it has long been desired to provide an electromechanical programmer/timer for appliance having a ratchet and pawl advance mechanism providing a relatively fast rate of advance and yet also provide for a substantially slower rate of advance with a continuous drive means for a portion of the selected program interval.